When Selecting Fibers for UHPC, How to Choose Between Metallic and Non-Metallic Fibers?

In UHPC material design, the choice of fibers directly affects the mechanical properties and application scenarios of the material. Based on 28 years of R&D experience in fiber-reinforced concrete, Qinglong Group believes that the choice between metallic and non-metallic fibers requires comprehensive consideration of multiple factors such as strength requirements, durability, cost, and application environment, as different fiber types each have their own advantages and application scenarios.

Metallic fibers, represented by steel fibers, are the most commonly used reinforcing fibers in UHPC. With a tensile strength typically exceeding 2000MPa and an elastic modulus of up to 200GPa, they can effectively improve the tensile strength and toughness of the material. Qinglong Group gives priority to copper-plated steel fibers in UHPC for load-bearing structures, with a diameter of 0.2mm, a length of 13mm, and a volume fraction of 2.5%. In the Shanghai Century Plaza project, the steel fiber-reinforced UHPC achieved a flexural strength of 25MPa and a fracture energy exceeding 30000J/m², meeting the safety requirements of large public buildings. However, steel fibers have the disadvantages of high density and susceptibility to corrosion, and their application in chloride ion environments requires additional anti-corrosion measures.

Non-metallic fibers mainly include carbon fibers, basalt fibers, and polymer fibers. Carbon fibers have excellent tensile strength (3000-5000MPa) and corrosion resistance, but their price is relatively high and their bonding performance with the cement matrix requires special treatment. Qinglong Group uses carbon fibers in special projects requiring resistance to magnetic interference, where a volume fraction of just 1.5% can achieve a reinforcing effect comparable to that of steel fibers. Basalt fibers have outstanding temperature resistance, but their elastic modulus is relatively low, making them suitable for high-temperature environments.

The geometric parameters of fibers have a significant impact on the reinforcing effect. The aspect ratio is an important parameter; the aspect ratio of steel fibers is usually controlled between 60 and 80 to ensure a good pull-out effect rather than fracture failure. Qinglong Group's test data show that when the aspect ratio increases from 40 to 80, the fracture energy of UHPC can be improved by more than 50%. The surface morphology of fibers also requires attention; hooked-end steel fibers provide better anchorage than straight ones.

In practical engineering, fiber selection also needs to take construction techniques into account. The spraying process requires fibers with good dispersibility, while casting can accommodate longer fibers. Through 28 years of technical accumulation, Qinglong Group has established a complete fiber selection database to provide optimal fiber reinforcement solutions for different projects.